1. Field of the Invention
The present invention relates to the reduction of carbon dioxide emissions from the exhaust gas stream of vehicles powered by internal combustion engines and other heat engines that produce waste heat.
2. Description of Related Art
The currently accepted thinking is that global warming is due to emissions of greenhouse gases such as carbon dioxide (CO2) and methane (CH4). About a quarter of global CO2 emissions are currently estimated to come from mobile sources, i.e., automobiles, trucks, buses and trains that are powered by internal combustion engines (ICEs). This proportional contribution is likely to grow rapidly in the foreseeable future with the projected surge in automobile and truck ownership in developing countries. At present, the transportation sector is a major market for crude oil, and controlling CO2 emissions is both an environmental responsibility and a desirable goal in order to maintain the viability of the crude oil market in the transportation sector in the face of challenges from alternative technologies, e.g., cars powered by electric motors and storage batteries. Regulations to limit CO2 emissions from the tail pipe have been enacted in many countries.
CO2 management from mobile sources presents many challenges including space and weight limitations, the lack of any economies of scale and the dynamic nature of the operation of the ICEs powering the mobile sources.
Prior art methods for the capture of CO2 from combustion gases have principally focused on stationary sources, such as power plants. Those that address the problem of reducing CO2 emissions from mobile sources employ either combustion using oxygen, provide no means for the regeneration and reuse of the CO2 capture agent, and/or make no use of waste heat recovered from the hot source. Combustion using oxygen requires an oxygen-nitrogen separation step which is more energy-intensive than separating CO2 from the exhaust gases and would be more difficult if attempted on board the vehicle.
The focus of CO2 capture technology has been on stationary or fixed sources. Processes have been developed that use amines and amine functionalized liquids and solutions to absorb CO2 at temperatures ranging from ambient up to about 80° C. At temperatures above 100° C., and particularly in the range of from about 130° C. to 300° C. that are encountered in vehicles powered by an ICE, the amine solutions exhibit low capacity for CO2 absorption. Thus, the high temperature of the ICE exhaust gas makes direct treatment to remove CO2 with liquid amine solutions impractical without cooling the exhaust gas.
The capture of CO2 from mobile sources has generally been considered too expensive, since it involves a distributed system with a reverse economy of scale. The prior solution to the problem has appeared to be impractical due to on-board vehicle space limitations, the additional energy and apparatus requirements and the dynamic nature of the vehicle's operating cycle, e.g., intermittent periods of rapid acceleration and deceleration.
It is therefore an object of the present invention to provide a method, a system and an apparatus which address the problems of efficiently and cost-effectively reducing the CO2 emissions from vehicles by temporary on-board storage of the CO2.
As used herein, the term “internal combustion engine,” or ICE, includes heat engines in which a carbon-containing fuel is burned to produce power or work and generates waste heat that must be removed or dissipated.
As used herein, the term “mobile source” means any of the wide variety of known conveyances that can be used to transport goods and/or people that are powered by one or more internal combustion engines that produce an exhaust gas stream containing CO2. This includes all types of motor vehicles that travel on land, as well as trains and ships where the exhaust gas from the ICE is discharged into a containing conduit before it is discharged into the atmosphere.
The term “vehicle” as used herein is to be understood as a convenient shorthand and synonymous with “mobile source” and is coextensive with “conveyances”, generally, as that term is used above.
As used herein, the terms “CO2 capture agent” and “capture agent” mean a phase-changing absorbent liquid or a solid adsorbent material having a magnetic core that has a predictable capacity to absorb or adsorb CO2 reversibly over a significant number of absorption/adsorption and desorption cycles.
As used herein, the term “waste heat” is the heat that a typical engine produces which is contained mainly in the hot exhaust gases ranging from about 300° C. to 650° C. and the hot engine coolant from about 80° C. to 120° C. in liquid coolant systems. Additional heat is emitted and lost by convection and radiation from the engine block and its associated components, and other components through which the exhaust gas passes, including the cylinders in air-cooled engines, the manifold, pipes, catalytic converter and muffler, and the engine's liquid coolant and the hot engine oil. This waste heat energy totals about 60-75% of the energy that typical hydrocarbon fuels provide.
The ICE can be air-cooled, in which case there will be no source of hot engine coolant. However, the engine block and associated metal components can provide the heat required to release the CO2 from, and thereby regenerate the CO2 capture agent. In the case of a manual gear shift as distinguished from an automatic transmission, there will be no source of hot transmission fluid.